Method of material deposition

ABSTRACT

A method and apparatus for material deposition onto a sample to form a protective layer composed of at least two materials that have been formulated and arranged according to the material properties of the sample.

This application is a continuation of U.S. application Ser. No.15/985,346, filed May 2, 2018, which is a divisional of U.S. applicationSer. No. 15/087,968 filed Nov. 6, 2015, which claims priority from U.S.provisional Application No. 62/252,308, filed Mar. 31, 2016, all ofwhich are hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to charged particle beam induceddeposition, and more particularly to precursor gas composition for FIBand SEM beam chemistry.

BACKGROUND OF THE INVENTION

In the prior art, it is known to deposit material onto a sample via ionbeam induced deposition (IBID), typically performed in a focused ionbeam (FIB) instrument, and electron beam induced deposition (EBID),usually performed in a scanning electron microscope (SEM) instrument.According to known methods, a sample is placed in an evacuable specimenchamber of a charged particle beam apparatus—typically either a FIBsystem or a SEM system. The charged particle (or other) beam is appliedto the sample surface in the presence of a deposition gas, oftenreferred to as a precursor gas. A layer of the precursor gas adsorbs tothe surface of the sample. The thickness of the layer is governed by thebalance of adsorption and desorption of the gas molecules on the samplesurface, which in turn depends on, for example, the partial gaspressure, the substrate temperature, and the sticking coefficient. Thethickness of the resultant layer can vary according to the application.

Material deposition can be performed with a variety of different gasprecursors depending on the application. For example, tungstenhexacarbonyl (W(CO)₆) gas may be used to deposit tungsten andnaphthalene gas may be used to deposit carbon. A precursor gas of TEOS,TMCTS, or HMCHS gas in combination with an oxidizer such as H₂O or O₂may be used to deposit silicon oxide (SiO_(x)). For deposition ofplatinum (Pt), a (methylcyclopentadienyl) trimethyl platinum gas may beused.

The material depositions obtained from these different precursors havedifferent properties. For example, IBID Pt material deposited using(methylcyclopentadienyl) trimethyl platinum precursor tend to be“softer.” That is, such softer materials are more susceptible tosubsequent ion beam sputtering than “harder” IBID carbon or tungstenlayers obtained with naphthalene or W(CO)₆, respectively. Silicon oxidelayers using a precursor of TEOS, TMCTS, or HMCHS gas in combination anoxidizer such as H₂O or O₂ tend to be more of a “medium” hardness. Therelative “hardness” or “softness” of the material is dependent on theangle of incidence of the beam. In some material pairs the “harder”material becomes softer at a differing angle of incidence. Otherdifferences exist as well. For example, when platinum films are used assacrificial caps prior to FIB cross-sectioning (such as occurs in TEMpreparation), the soft nature of the film tends to result in smoothcross-sectional cut face. By contrast, carbon films are extremely hardand tend to produce artifacts on the cut face known as “curtaining.” Inaddition to hardness properties the growth rates of these differentdeposition precursors may also be a significant factor for variousapplications.

The following are examples of gas precursors of various classes. Forexample, class C etchants may include oxygen (O₂), nitrous oxide (N₂O),and water. Metal etchants may include iodine (I₂), bromine (Br₂),chlorine (Cl₂), xenon difluoride (XeF₂), and nitrogen dioxide (NO₂).Dielectric etchants may include xenon difluoride (XeF₂), nitrogentrifluoride (NF₃), trifluoroacetamide (TFA), and trifluoroacetic acid(TFAA). Metal deposition precursor gases may include(methylcyclopentadienyl) trimethyl platinum, tetrakis(triphenylphosphine) platinum (0), what is (0) tungsten hexacarbonyl(W(CO)₆), tungsten hexafluoride (WF₆), molybdenum hexacarbonyl(Mo(CO)₆), dimethyl (acetylacetonate) gold (III), tetraethylorsosilicate(TEOS), and tetraethylorsosilicate (TEOS) plus water (H₂O). Dielectricdeposition precursors may include tetraethylorsosilicate (TEOS),tetraethylorsosilicate (TEOS) plus water (H₂O),hexamethylcyclohexacyloxane ((HMCHS)+O₂), andtetramethylcyclotetrasiloxane ((TMCTS)+O₂). Carbon deposition precursorsmay include naphthalene and dodecane (C₁₂H₂₆), and planar delayeringagents may include methylnitroacetate. Although these are many examplesof available gas precursors many others exist and are available for use.

Beam induced deposition is used in a wide variety of applications fordepositing a material onto a target surface of a sample such as asemiconductor wafer. The materials are deposited for a variety ofreasons such as to form thin-film surfaces, electrical connections,protective coatings for semiconductor feature characterization andanalysis, and capping material for milling high-aspect ratio structures(such as vias). However, when there is a significant difference betweenthe hardness of the sample and the deposited capping material, it can bedifficult to obtain the desired structure, shape, and surfacecharacteristics of a prepared sample. For example, it can be difficultto control sloped surfaces in the formation of milled structures,because the differential sputter rates of the materials can cause slopechanges at the interface between the materials. Additionally, artifactscan occur on FIB milled surfaces during a cross-sectioning process forpreparing samples for feature characterization and analysis.

Techniques using FIB systems are known for preparing ultra-thin samplesfor feature characterization and analysis in which it is important tominimize the occurrence of surface artifacts introduced during themilling process.

As semiconductor geometries continue to shrink, manufacturersincreasingly rely on transmission electron microscopes (TEMs) formonitoring the manufacturing process, analyzing defects, andinvestigating interface layer morphology. Transmission electronmicroscopes allow observers to see features having sizes on the order ofnanometers. In contrast to scanning electron microscopes (SEMs), whichonly image the surface of a material, TEMs also allow analysis of theinternal structure of a sample. In a TEM, a broad beam impacts thesample and electrons that are transmitted through the sample aredetected to form an image of the sample. A scanning transmissionelectron microscope (STEM) combines the principles of a TEM and SEM andcan be performed on either instrument. The STEM technique scans a veryfinely focused beam of electrons across a sample in a raster pattern.The sample must be sufficiently thin to allow many of the electrons inthe primary beam to travel through the sample and exit on the oppositeside.

Because a sample must be very thin for viewing with transmissionelectron microscopy (whether TEM or STEM), preparation of the sample canbe delicate, time-consuming work. The term “TEM” as used herein refersto a TEM or a STEM and references to preparing a sample for a TEM areunderstood to also include preparing a sample for viewing on a STEM. Theterm “STEM” as used herein also refers to both TEM and STEM.

There are several methods for preparing a thin sample for viewing with aTEM or STEM. Some methods entail extracting a sample without destroyingthe entire material from which the sample is extracted. Other methodsrequire destroying the material to extract the sample. Some methodsprovide extraction of a thin sample referred to as a lamella. Thelamella may require thinning before TEM or STEM viewing.

Lamella samples for TEM viewing are typically less than 100 nm thick,but for some applications samples must be considerably thinner. Withadvanced semiconductor manufacturing processes at design nodes of 30 nmand below, the sample needs to be less than 20 nm in thickness in orderto avoid overlap among small scale structures. Some applications, suchas analysis of next-node semiconductor devices, require lamellae havinga thickness of 15 nm or less to isolate specific devices of interest.Current methods of thinning lamellae are difficult and not robust.Thickness variations in the sample result in sample bending or bowing,overmilling, or other catastrophic defects that may destroy the lamella.For such thin samples, preparation is a critical step in TEM analysisthat significantly determines the quality of structural characterizationand analysis of the smallest and most critical structures.

It is known to provide a protective layer deposited over the desiredlamella location before thinning to protect the region of interest onthe sample from exposure to the ion beam and to prevent bending orbowing. In one commonly used preparation technique as seen in FIGS. 1-3,a protective layer 22 of a material such as tungsten, carbon, orplatinum is first deposited over the area of interest on a top surface23 of a sample body as shown in FIG. 1 using electron beam or ion beamdeposition. Next, as shown in FIGS. 2 and 3, a focused ion beam using ahigh beam current with a correspondingly large beam size is used to milllarge amounts of material away from the front and back portion of theregion of interest. The remaining material between the two milled areas24 and 25 forming a thin vertical sample section 26 that includes anarea of interest. Typically, the area of interest is contained in thetop 200-300 nm below the sample surface. The area 25 milled on the backside of the region of interest is shown smaller that the front area 24.The smaller milled area 25 is basically to save time, but also preventsthe finished sample from falling over into larger milled area 24 makingit difficult to remove the sample section 26 from the sample body.Sample section 26 may then be cut away from the sample body using afocused ion beam and then lifted out using, for example, amicromanipulator, in a well-known manner. The sample section 26 is thentypically transferred to a TEM grid and thinned. The sample section 26may then be analyzed using a TEM or other analytical tools.

Significant problems occur in the preparation of ultra-thin (<30 nmthick) TEM samples. For example, a protective layer of platinum over thearea of interest is too soft and often fails during lamella thinning,becoming completely consumed by peripheral erosion from the ion beamtails before the lamella thinning is complete. Layers of hardermaterials may resist erosion better than softer materials, but may causeundesirable artifacts on the cross-sectional face of the lamella.

FIGS. 4 and 5 show examples of problems in the preparation of ultra-thinsamples. As seen in FIG. 4, a cross-section of a lamella sample 30 isshown prepared with a soft Pt cap 32 deposited on a hard diamondsubstrate 34. When the lamella 30 is prepared by thinning to therequired thickness dimension, this hardness mismatch results in fastererosion of the softer Pt cap 32 than the harder diamond substrate 34.This combination would prevent the user from thinning the lamella asmuch as desired, because the protective cap 32 would eventually becompletely consumed before the substrate 34 was adequately thinned.Conversely, as seen in FIG. 5, a cross-section of a lamella sample 36 isshown prepared with a hard carbon cap 38 placed on a soft coppersubstrate 40. In this example, undercutting 42 may be observed becausethe softer substrate 40 is consumed faster than the harder cap 38. Thiscan lead to premature failure of the lamella, as well ascross-sectioning surface artifacts, such as “curtaining.”

Curtaining is an artifact that causes the surface of a sample to berippled or uneven. Curtaining may arise for a variety of reasons. If thesample is non-homogeneous, consisting of different materials withdifferent sputter rates, then the harder materials may form resistantareas that project slightly from the cross-sectional face. Theseprojections shield regions below them, leading to vertical streaks thatpropogate downwards. FIG. 6 shows a sample 44 having a silicon substratewith a tungsten protective layer exhibiting curtaining. The “curtains”arise because the tungsten is harder or more resistant to sputteringfrom the ion beam than the silicon substrate. This leads to featuresthat protrude slightly from the cross-sectional face of the substrate.The harder, overhanging tungsten basically shields the substratedirectly below it leaving vertical projections of the tungsten.Alternatively, some hard capping materials form ripple-like orrectilinear patterns when exposed to the ion beam, even though thecapping material is itself internally homogenious. FIG. 7 shows a sample46 having a silicon substrate with a carbon protective layer exhibitingcurtaining. When a cross-sectional mill is performed, the carbon layermaterial gradually assumes a highly textured surface. Thus, thetopography of the carbon layer leads to curtaining in this example.Top-down thinning of a sample having these types of structural ordensity variations will cause vertical ridges or variations to propagatefrom the denser materials (i.e., metal lines) near the top of the sample(the top being defined as closest to the ion beam source) down the faceof the cross-section, running in a direction parallel to the ion beamdirection. Curtaining is most often observed in semiconductor materialswhere multiple patterned layers of materials having a low sputteringyield blocks a faster sputtering yield material. Curtaining may also beobserved in materials exhibiting different topographic regions wherechanges in sputtering yields vary with the milling incident angle.Samples with voids also induce curtains. Curtaining artifacts reduce thequality of the TEM imaging and limit the minimal useful specimenthickness.

Another type of artifact is referred to as a “golf tee.” For example, alayer of either tungsten or carbon on top of a region of interest on asample, which is typically a material such as silicon. The cappingmaterial and the silicon substrate have different “hardnesses,”(resistance to sputtering from the ion beam) resulting in atop-to-bottom thickness variation called a “golf-tee”, wherein thesample is thicker at the top and narrows to a thinner dimension so thatthe sample has a “golf tee” profile when observed in a Y-section. Sincethe region of interest is usually contained near the top surface of thelamella the thicker dimension can obscure the region of interest andcause a less than desirable sample for TEM viewing.

An example of a “golf-tee” effect can be seen in FIG. 8, which shows aTEM sample 50 with an ion beam induced deposition (IBID) tungstenprotective layer 52 located on the top surface of sample 50. In thisexample, after thinning the sample 50 is 44 nm wide directly underprotective layer 52 and narrows to 25 nm wide at 150 nm below protectivelayer 52. This thickness variation is the result of the differentialetch rate between the silicon substrate and the tungsten protectivelayer. Tungsten is a harder, denser material than silicon and has asignificantly lower etch rate, which causes the tungsten protectivelayer 52 to be wider than the lamella body. Typically, the region ofinterest is located in the general area where the “golf-tee” occursobscuring or interfering with the region of interest for TEM viewing.

What is needed is an improved method of material deposition to obtain acontrolled work piece surface that is free of surface artifacts andslope changes.

Summary of the Invention

It is an object of the invention to provide an improved method ofmaterial deposition that combines the properties of at least twoprecursors for reducing surface artifacts and slope changes.

In accordance with one preferred embodiment, a material deposition iscarried out to provide a protective material layer having a sputter ratethat substantially matches the sputter rate of the substrate material. Acharged particle beam is directed toward the substrate in a vacuumchamber of a FIB system to induce material deposition from a precursorgas mixture. Resistance to sputtering of the protective layer materialdeposition can be adjusted by changing the ratio of the gas mixturecomponents. A multiple gas injecting system is used having variable flowcontrol and mixing capabilities that can vary the precursor ratios overa wide range to vary the hardness of the protective layer materialdepending on the material of the sample substrate.

In accordance with another preferred embodiment, material deposition iscarried out to provide a protective layer that includes two or morematerial compositions deposited in layers with each layer havingdifferent etch rates. Preferably, a charged particle beam is directedtoward the substrate in a vacuum chamber of a FIB system to inducedeposition from a precursor gas of a first protective layer onto thesample substrate above the region of interest. An ion beam is thendirected toward the sample substrate to induce deposition from aprecursor gas of at least a second protective layer on top of the firstprotective layer. Preferably, the first protective layer has an etchrate that closely matches the etch rate of the sample and the secondprotective layer (and any further layers) has an etch rate that isdifferent than the etch rate of the sample. For example, for a softersubstrate, a softer protective material may be first deposited to be indirect contact with the substrate and then a second harder layer may bedeposited on top of the first layer. The harder layer will resisterosion from the ion beam while the softer bottom layer will preventcross-sectioning artifacts. A bottom layer that has a sputter rate thatclosely matches the sputter rate of the substrate lessens the risk ofcross-sectioning artifacts. For harder substrates such as diamond,carbon, or silicon carbide, a harder protective layer may be firstdeposited to be in direct contact with the substrate with a softermaterial layer deposited on top of the first layer.

In another preferred embodiment, material deposition is carried out toprovide alternating layers of material to form the protective layer inwhich the etch rate of the protective layer material is “tuned” bydepositing the alternating, thin layers of material using discrete gaschemistries, which forms an alternating “parfait-like” macrostructurewith an etch rate that is between the etch rates of the individualcomponents. By adjusting the thickness of the individual components, aswell as the total number of layers, the user may achieve some degree oftunability, to achieve the desired film property. A limiting extreme ofinfinite ultrathin alternating layers could be deposited resulting in adeposition resembling a composite mix.

In another preferred embodiment, a mixture of gas precursors is used inmaterial deposition, but the ratio of the gases is gradually adjustedduring the course of the deposition to create a composite cappingmaterial, such that the bottom of the protective layer is mostly onecomponent and the top of the layer is mostly another component, withintermediate regions having intermediate compositions. This provides agradual transition from hard to soft (or vice-versa), as the millprogresses through the protective material.

In another preferred embodiment, the material deposition methodsdescribed herein may be performed with TEM lamella preparation fortuning the hardness of the sacrificial protective cap to prevent lamellafailure due to erosion from the beam tails, and can minimizecross-sectioning artifacts such as curtaining and sidewall slope changesat interfaces.

In yet another preferred embodiment, the material deposition methodsdescribed herein may be performed with applications in which a compositecapping layer is used to create single-sided FIB cross-section ingeneral, with a cut face that is free of defects and slope changes.

In still another preferred embodiment, the material deposition methodsdescribed herein may be performed with applications in which compositiondeposition films can be used to control the milled profile ofhigh-aspect ratio structures (such as vias) that are created with ionbeam milling.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter. It should be appreciated by those skilled in the art thatthe conception and specific embodiments disclosed may be readilyutilized as a basis for modifying or designing other structures forcarrying out the same purposes of the present invention. It should alsobe realized by those skilled in the art that such equivalentconstructions do not depart from the scope of the invention as set forthin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee. For a more thorough understanding of the presentinvention, and advantages thereof, reference is now made to thefollowing descriptions taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1-3 illustrate the steps in an ex-situ sample preparationtechnique according to the prior art.

FIG. 4 shows a prior art lamella profile having a hard diamond substrateand an easily consumable soft platinum top layer.

FIG. 5 shows a prior art lamella profile having a soft copper substrateand hard carbon top layer with resulting undercutting.

FIG. 6 is a photomicrograph of a FIB cross-sectional face with atungsten top layer showing curtaining according to the prior art.

FIG. 7 is a photomicrograph of a thinned TEM sample with a carbon toplayer showing curtaining according to the prior art.

FIG. 8 shows an image of a lamella after thinning with a “golf-tee”artifact according to the prior art.

FIG. 9 shows schematically a charged particle beam system with amultigas injection system (MGIS).

FIG. 10 shows a contour plot of vertical deposition growth rate as afunction of the valve duty cycles for the Pt precursor (X axis) and Cprecursor (Y axis).

FIG. 11 shows a contour plot of sputter rates of deposited C—Ptcomposite materials as a function of valve duty cycles for the Ptprecursor (X axis) and C precursor (Y axis).

FIG. 12 shows a lamella profile with a C-rich protective compositelayer.

FIG. 13 shows a lamella profile with a Pt-rich protective compositelayer.

FIG. 14 shows a lamella profile with a C—Pt protective composite layer.

FIG. 15 shows an embodiment of composite material deposition for asubstrate having formed vias structures.

FIG. 16 shows another embodiment of composite material deposition for asubstrate having formed vias structures.

FIG. 17 shows another embodiment of composite material deposition for asubstrate having formed vias structures.

FIG. 18 shows the valve duty cycle for the composite material depositionof FIG. 17.

FIG. 19 shows yet another embodiment of composite material depositionfor a substrate having formed vias structures.

FIG. 20 shows the valve duty cycle for the composite material depositionof FIG. 19.

FIG. 21 shows another embodiment using a dual beam system of the typefor carrying out the present invention.

FIG. 22 shows a lamella profile with a protective layer of distinctmaterials.

FIG. 23 shows a lamella profile with a protective layer of multipledistinct materials.

FIG. 24 shows a lamella profile with a protective layer of distinctalternating material.

FIG. 25 shows an image of a preferred embodiment of a lamella havingmultiple protective layers.

FIG. 26 shows a photomicrograph of another preferred embodiment of alamella having multiple protective layers.

FIGS. 27A and 27B show a plot of the data from Table 1 and 2.

FIG. 28 shows a flow chart for material deposition according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the invention provide a method for improved method ofmaterial deposition onto a work piece that combines the properties of atleast two precursors for reducing surface artifacts and slope changes.

According to a first preferred embodiment of the present invention, asubstrate, such as a semiconductor wafer, is loaded into a dual-beamFIB/SEM system having both a FIB column and a SEM column. Although adual-beam system is discussed it is to be understood that other FIBsystems may be used to carry out the invention. Wafers may betransferred manually or are preferably transferred by way of amulti-wafer carrier and auto-loading robot (not shown).

In applications for preparing lamella samples the location of a regionon the sample containing a feature of interest for extraction andanalysis (i.e., the lamella site) is determined. For example, thesubstrate may be a semiconductor wafer or portion thereof and the sampleto be extracted may include a portion of an integrated circuit that isto be observed using the TEM. Typically, the substrate is coarselyaligned by using machine vision to locate reference marks on the waferor wafer piece, or using the edges and alignment notch or flat of anunpatterned wafer. Alternately, a lamella site may be locatedautomatically using image recognition software. Suitable imagerecognition software is available from Cognex Corporation of Natick,Mass. Image recognition software can be “trained” to locate the desiredlamella locations by using sample images of similar features or by usinggeometric information from CAD data. Automated FIB or SEM metrology canalso be used to identify or help identify the lamella site. Metrologymay consist of image-based pattern recognition, edge finding, ADR,center-of-mass calculations, or blobs. If desired, fiducial marks may bemilled into the substrate surface as a precise and accurate locatingmark.

A composite protective layer is then deposited over the lamella site toprotect the sample. In a first preferred embodiment, an IBID or EBIDdeposition can be performed using a multiple gas injection system inwhich two or more precursor gases flow simultaneously. For example, adeposition may be performed in which the deposited material hasproperties intermediate to the two individual components. For example,an IBID deposition obtained with mixtures of Pt and C precursors may beperformed to obtain a protective layer having properties intermediatebetween the properties obtained with the Pt and C precursorsindividually. Precursor mixing can be performed in numerous ways. Forexample, a single gas nozzle outlet can be shared by two or more vesselscontaining individual chemical precursors, and the relative flow ratesof the individual components can be controlled by pulsed valves situatedbetween the chemical precursor container and the outlet.

FIG. 9 shows a schematic of a beam system 100 incorporating anembodiment of the invention. Beam system 100 includes a sample vacuumchamber 102 containing a sample stage 104 for supporting a work piece106 to be processed by a beam 110, which is produced by a beam producingsubsystem, such as a laser or a charged particle beam column. Forexample, a charged particle beam column 112 includes a charged particlesource 113, one or more focusing lenses 114, and a deflector 116 forscanning or otherwise directing the beam 110 in a designated pattern onthe work piece surface. An evacuation system, such as a combination of ahigh vacuum turbo pump 120 and a backing pump 122, maintains a vacuum ofpreferably less than 10⁻³ mbar more preferably less than 10⁻⁴ mbar, andeven more preferably less than or equal to about 10⁻⁵ mbar in samplevacuum chamber 102 during processing. Backing pump 122 exhausts to anexhaust outlet 124.

Gas is supplied to a local area at the work piece surface by aretractable needle 130 that extends from a multiple gas injection system(MGIS) valve 132, which is described in more detail below. Gases, suchas deposition precursor gases, etch precursor gases, or inert purgegases, are stored in gas reservoirs 131. The term “reservoir” is usedbroadly to include any gas source. Some of reservoirs 131 may includesolid or liquid materials that are heated, for example, in a crucible,to evolve the desired gas, while other reservoirs 131 may includecompressed gases. Each reservoir 131 is connected to MGIS valve 132 by acorresponding conduit 133, with a regulating valve 134 and a stop valve136 in the flow path between each reservoir 131 and MGIS valve 132.While FIG. 9 shows two reservoirs with corresponding conduits, theinvention is not limited to any number of reservoirs. Some embodimentsof the invention use six or more reservoirs, while other embodiments mayuse a single gas source.

When a pre-set gas recipe is executed, the MGIS valve 132 needle 130 isextended and process gases flow from the valve 132 through needle 130 tothe surface of work piece 106 near the point at which charged particlebeam 110 is focused.

Sample stage 104 is used to position the work piece beneath the chargedparticle beam 110 and the needle 130. Gases from needle 130 in thesample vacuum chamber are eventually pumped from the chamber by a turbopump 120. Vacuum pump 138 removes remaining gases from the interior ofthe MGIS valve through MGIS vacuum conduit 140, which is equipped withMGIS vacuum valve 142.

The specific recipe for the composite protective layer consists ofmixing precursors in specific ratios depending on the material of thesample substrate. Preferably, one of the precursors will yield arelatively soft deposition material, and the other precursor will yielda relatively hard deposition material. Therefore, a user can tune thehardness of the deposition layer to be anything in between theproperties of each individual precursor. The precursors are mixed insuch a ratio to match the sputter rate of the protective layer materialto the sputter rate of the substrate material to enable adequatethinning and to prevent interface artifacts. The duty cycles of thevalves in the MGIS delivery hardware can be continuously varied between0% and 100%. Therefore, a deposition material can be adjusted to haveproperties intermediate between those of the individual mixed precursorcomponents. This allows customized deposition to different substratematerials and different applications.

In one example, a protective carbon-platinum (C—Pt) layer is deposited.The C—Pt precursors are mixed in a specific ratio depending on thematerial of the substrate. This is achieved by adjusting the C—Pt ratio,as indicated in the contour plots as seen in FIGS. 10 and 11. In FIG.10, a contour plot 150 of vertical deposition growth rate (nm/sec) as afunction of the valve duty cycles for the Pt precursor (X axis) and Cprecursor (Y axis) is shown. The highest growth rate is indicted by thegreen circle 152, and growth rates of standard single-precursormaterials are indicated by the gray 154 and black 156 circles for Pt andC, respectively. In FIG. 11, a contour plot 160 of sputter rates ofdeposited C—Pt composite materials as a function of valve duty cyclesfor the Pt precursor (X axis) and C precursor (Y axis) is shown. Thesputter rates of the standard single-precursor materials are indicatedby the gray 162 and black 164 circles for Pt and C, respectively. Addinga small amount of Pt to a mostly C deposition, the conditions marked bythe green circle 166, for example, results in a material that issuperior as a protective cap layer than either individual component. Thelayer is much harder than Pt alone but does not have the curtainingeffects of C alone. The variable duty cycle valve control, or percentageof “on” time of the pulsed valves, and mixing capability of the multiplegas injection system enables such adjustment. Thus, a desired “hardness”can be achieved by moving along the dotted line in FIG. 11. Therefore, auser may customize the hardness of the deposited layer to suit thesample, and especially to match the hardness of the sample substrate.

For example, as seen in FIGS. 12-14, a C—Pt composite materialdeposition having various hardness properties is carried out onto asubstrate. For example, a C—Pt composite material can be formed onto asubstrate 200 by continuously adjusting the valve duty cycle to achievea C-rich composite (C valve duty cycle=80%, Pt valve duty cycle <2%),resulting in a very hard protective layer 202 (but not as hard as Calone) as seen in FIG. 12. As seen in FIG. 13, a C—Pt composite materialcan be formed onto a substrate 206 by continuously adjusting the valveduty cycle to achieve a Pt-rich composite (C valve duty cycle <2%, Ptvalve duty cycle=80%), resulting in a very soft protective layer 208(but not as soft as Pt alone). If a hard substrate sample is used, suchas diamond, a C-rich layer having a hardness that closely matches thehardness of the diamond substrate may be deposited. As an example seenin FIG. 14, a substrate 210 having protective layer of C—Pt material 212deposited with an MGIS setting of 80%-5% (C to Pt) is preferable to alayer obtained with either pure C or pure Pt precursors. An 80%-5% ratiohas a higher material growth rate than individual C or Pt used alone.Additionally, this ratio has a higher sputter resistance than Pt and hasfewer curtaining artifacts than C.

Other depositions may be obtained for substrates having various hardnessproperties. For example, a protective layer with intermediate dutycycles, (for example, 40% for both carbon and platinum), will haveproperties approximately intermediate to the properties obtained witheither individual component. For samples with softer substrateproperties, such as an organic resin, the deposition precursor may beadjusted to be Pt rich.

Possible duty cycle and sample combinations include a medium hardsilicon substrate with a deposition layer using a valve duty cycle of50%-50% (C to Pt), a hard diamond substrate with a deposition layerusing a valve duty cycle of 80%-1% (C to Pt), and a soft resin substratewith a deposition layer using a valve duty cycle of 5%-80% (C to Pt).The precursors can be mixed with a conventional MGIS system as well inwhich the ratio of the precursors could be adjusted crudely bycontrolling the crucible temperature of each agent. However, many dutycycle combinations are possible and these examples illustrate that thehardness of the deposited material can be continuously varied to matchthe hardness of the substrate material.

In addition to the pulsed valve mixing strategy described above, otherprecursor delivery methods may be used. For example, the relative flowrates of individual precursor components can be adjusted with mass flowcontrol valves, metering needle valves, or simply by adjusting thetemperature of the precursor's container to adjust the vapor pressure ofthat component. Flow rates can also be affected by using orifices(apertures) of different sized, or by using tubing with different innerdiameters. Finally, it is possible to mix multiple precursor chemicalsin the same vessel, such that opening a single valve admits a mixture ofprecursor gases into the instrument's vacuum chamber. Regardless of thedelivery strategy used to deliver the multi-component precursor mixture,precursor mixtures can be used to tune the properties of the depositedmaterial layer regardless of the hardware or system for creating themixture.

Deposition material layers from precursor mixtures can be applied for avariety of different applications. In TEM lamella preparation, tuningthe hardness of the sacrificial protective cap can prevent lamellafailure due to erosion from the beam tails, and can minimizecross-sectioning artifacts such as curtaining and golf-tee as well assidewall slope changes at interfaces. Another application for compositematerial deposition is for use to create single-sided FIB cross-sectionin general, with a cut face that is free of defects and slope changes.

Composite deposition layers can also be used to control the milledprofile of high-aspect ratio structures (such as vias) that are createdwith ion beam milling. This may be useful for FIB nano- andmicro-fabrication, or for ion-beam lithography techniques. In thisapplication as seen in FIG. 15, a workpiece 250 includes a thincomposite deposition capping material 252 deposited onto a substrate 254into which the user wants to create the high-aspect ratio structure suchas via 256. The specific recipe for the composite deposition should bechosen to be “harder” than the underlying target material. As the millinitially progresses, the ion beam will penetrate deeper and deeper intothe hard deposition layer 252. Eventually, the mill will reach theinterface between the hard deposition 252 and the soft underlyingsubstrate 254. At this point, the underlying substrate 254 will begin tobe milled, but only in the center of the ion beam profile, where themilling speed was highest. Because the underlying substrate 254 issofter than the capping material 252, and because the ion beam profileis approximately Gaussian, the soft material 254 should be rapidlymilled by the intense center of the ion beam distribution, while theless intense “tails” of the ion beam still have not penetrated theharder capping material 252.

Thus, the arrangement of a harder capping film on top of a softer targetmaterial has a sharpening effect on the shape of the ion milling probe,and it is possible to obtain vias with narrower dimensions that would bepossible to achieve with an uncapped substrate. If desired, the topcapping film could be removed in a final step, leaving the “sharpened”high aspect ratio mills behind. This could be achieved, for example, byusing a hard carbon film over a silicon substrate, and the carbon filmcould be removed with an oxygen plasma cleaning step. Thus, a highaspect ratio structure with relatively narrow dimensions and parallelsidewalls may be formed.

In another example, a via with a chamfered or tapered profile (flaredopen at the top) may be formed by depositing a capping film that issofter than the underlying substrate. In this example seen in FIG. 16, aworkpiece 260 is shown with a capping layer 262 that is softer than theunderlying substrate 264 formed with a via 266. The effect of the beamtails on the soft capping layer 262 will create more lateral erosion,resulting in a pronounced widening at the top of the via structure, ascompared to a via milled without a cap.

FIG. 17 shows an embodiment of a workpiece sample 280 with a siliconsubstrate 281 with a composite layer 282 in which FIB-milled vias 283are created wherein the composite layer 282 has a “hardness” that variesfrom bottom to top of the layer. Such a composite layer can be createdby adjusting the duty cycle of the individual precursor componentsduring the course of the deposition. For example, a Pt—C composite layerthat varies from soft-to-hard (bottom-to-top) could be deposited bybeginning the deposition with a Pt-rich mixture, and graduallytransitioning to a C-rich mixture as the deposition grows. The valveduty cycle for such a process is shown in FIG. 18 by graph 286.

FIG. 19 shows a reverse process with a workpiece sample with a siliconsubstrate 291 having a composite layer 292 in which FIB-milled vias 293are created wherein the composite layer 292 has a “hardness” that variesfrom bottom to top of the layer. Such a composite layer can be createdby adjusting the duty cycle of the individual precursor componentsduring the course of the deposition. For example, a Pt—C composite layerthat varies from hard-to-soft (bottom-to-top) could be deposited bybeginning the deposition with a C-rich mixture, and graduallytransitioning to a Pt-rich mixture as the deposition grows. The valveduty cycle for such a process is shown in FIG. 20 by graph 296.

Although Pt—C mixtures have been discussed as examples of compositelayers, it should be understood that other precursor combinations resultin deposition layers with variable material properties as well. Forexample, a carbon-platinum composite may be obtained with precursors ofnaphthalene and (methylcyclopentadienyl) trimethyl platinum. Acarbon-tungsten composite may be obtained using naphthalene and W(CO)₆precursors. Precursors of (methylcyclopentadienyl) trimethyl platinumand W(CO)₆ may be used to obtain a platinum-tungsten composite and acarbon-SiO_(x) composite may be obtained with precursors of naphthaleneand TEOS or TMCTS or HMCHS.

It is possible to adjust the “hardness” of dielectric depositions, whichare typically performed with a siloxane-based precursor and an oxidizer.A high concentration of oxidizing agent will lead to a deposition layerwith the fully-saturated SiO₂ stoichiometry, whereas a layer depositedwith a depleted amount of oxidizer will not be fully saturated, and willhave a stoichiometry SiO_(x), with X<2. Any of the followingsiloxane-oxidizer combinations is suitable for such tuning: TEOS(tetraethylorthosilicate) and O₂; TMCTS (tetramethylcyclotetrasiloxane)with N₂O; and HMCHS (hexamethylcyclohexasiloxane) and water. However,any of the siloxanes can be used with any of the oxidizers.

Plasma FIB instruments which generate any of the following primary ions:O⁺, O₂ ⁺, O₃ ⁺, N⁺, N₂ ⁺, H₂O⁺, H₂O₂ ⁺, N₂O⁺, NO⁺, NO₂ ⁺; canpotentially be used in conjunction with a siloxane precursor to depositdielectric layers with variable hardness. In this case the oxidizingagent is the primary beam species itself. Thus, the deposited layers canbe made to range from the fully saturated SiO₂ stoichiometry to aless-saturated SiO_(x) (X<2) stoichiometry by adjusting the beam currentdensity, precursor flux, and/or ion beam energy during the depositionprocess.

It should be understood that although the above examples discussmodulating material “hardness,” or resistance to sputtering from an ionbeam, other material properties are also adjustable using the samemethods. For example, the resistivity of dielectric films will increasewith increasing oxidizer concentration. Thus, by controlling thesiloxane-oxidizer mixture the user can deposit films with more or lesselectrical conductivity. The optical transparency of deposited films isanother property that can be modulated by precursor mixing.Additionally, material deposition using the disclosed methods may beobtained by laser-assisted precursor decomposition or by thermaldecomposition on a heated surface.

According to a second preferred embodiment of the present invention, asubstrate, such as a semiconductor wafer, is loaded into a dual-beamFIB/SEM system having both a FIB column and a SEM column. A typicaldual-beam system configuration includes an electron column having avertical axis and an ion column having an axis tilted with respect tothe vertical (usually at a tilt of approximately 52 degrees). One suchsystem is the Helios family of DualBeam™ Systems, commercially availablefrom FEI Company of Hillsboro, Oreg., the assignee of the presentinvention.

FIG. 21 shows a typical dual-beam FIB/SEM system 2110, suitable forpracticing the present invention. System 2110 includes an evacuatedenvelope having an upper neck portion 2112 within which are located aliquid metal ion source 2114 or other ion source and a focusing column2116. Other types of ion sources, such as multicusp or other plasmasources, and other optical columns, such as shaped beam columns, couldalso be used, as well as electron beam and laser systems.

An ion beam 2118 passes from liquid metal ion source 2114 through ionbeam focusing column 2116 and between electrostatic deflection meansschematically indicated at deflection plates 2120 toward a substrate orwork piece 2122, which comprises, for example, a semiconductor devicepositioned on stage 2124 within lower chamber 2126. Stage 2124 can alsosupport one or more TEM sample holders, so that a sample can beextracted from the semiconductor device and moved to a TEM sampleholder. Stage 2124 can preferably move in a horizontal plane (X and Yaxes) and vertically (Z axis). In some systems, stage 2124 can also tiltapproximately sixty (60) degrees and rotate about the Z axis. A systemcontroller 2119 controls the operations of the various parts of FIBsystem 2110. Through system controller 2119, a user can control ion beam2118 to be scanned in a desired manner through commands entered into aconventional user interface (not shown). Alternately, system controller2119 may control FIB system 2110 in accordance with programmedinstructions stored in a computer readable memory, such as a RAM, ROM,or magnetic or optical disk. The memory can store instructions forcarrying out the methods described above in an automated orsemi-automated manner. Images from the SEM can be recognized by thesoftware to decide when to continue processing, when to stop processing,and where to locate the beam for milling.

For example, a user can delineate a region of interest on a displayscreen using a pointing device, and then the system could automaticallyperform the steps described below to extract a sample. In someembodiments, FIB system 2110 incorporates image recognition software,such as software commercially available from Cognex Corporation, Natick,Mass., to automatically identify regions of interest, and then thesystem can manually or automatically extract samples in accordance withthe invention. For example, the system could automatically locatesimilar features on semiconductor wafers including multiple devices, andtake samples of those features on different (or the same) devices.

An ion pump 2128 is employed for evacuating upper neck portion 2112. Thelower chamber 2126 is evacuated with turbomolecular and mechanicalpumping system 2130 under the control of vacuum controller 2132. Thevacuum system provides within lower chamber 2126 a vacuum of betweenapproximately 1×10⁻⁷ Torr (1.3×10⁻⁷ mbar) and 5×10⁻⁴ Torr (6.7×10⁻⁴mbar). For the deposition precursor gas or if an etch-assisting gas oran etch-retarding gas is used, the chamber background pressure may rise,typically to about 1×10⁻⁵ Torr (1.3×10⁻⁵ mbar).

High voltage power supply 2134 is connected to liquid metal ion source2114 as well as to appropriate electrodes in ion beam focusing column2116 for forming an approximately 1 keV to 60 keV ion beam 2118 anddirecting the same toward a sample. Deflection controller and amplifier2136, operated in accordance with a prescribed pattern provided bypattern generator 2138, is coupled to deflection plates 2120 whereby ionbeam 2118 provided by pattern generator 2138, is coupled to deflectionplates 2120 whereby ion beam 2118 may be controlled manually orautomatically to trace out a corresponding pattern on the upper surfaceof work piece 2122. In some systems the deflections plates are placedbefore the final lens, as is well known in the art. Beam blankingelectrodes (not shown) within ion beam focusing column 2116 cause ionbeam 2118 to impact onto blanking aperture (not shown) instead of target2122 when a blanking controller (not shown) applies a blanking voltageto the blanking electrode.

The liquid metal ion source 2114 typically provides a metal ion beam ofgallium. The source typically is capable of being focused into a subone-tenth micrometer wide beam at work piece 2122 for either modifyingthe work piece 2122 by ion milling, enhanced etch, material deposition,or for the purpose of imaging the work piece 2122. If desired, a chargedparticle detector 2140 can be used for detecting secondary ion orelectron emission to be connected to a video circuit 2142 that suppliesdrive signals to video monitor 2144 and receiving deflection signalsfrom controller 2119.

The location of charged particle detector 2140 within lower chamber 2126can vary in different embodiments. For example, a charged particledetector 2140 can be coaxial with the ion beam and include a hole forallowing the ion beam to pass. In other embodiments, secondary particlescan be collected through a final lens and then diverted off axis forcollection. A scanning electron microscope (SEM) 2141, along with itspower supply and controls 2145, are optionally provided with the FIBsystem 2110.

A gas delivery system 2146 extends into lower chamber 2126 forintroducing and directing a gaseous vapor toward work piece 2122. U.S.Pat. No. 5,851,413, to Casella et al. for “Gas Delivery Systems forParticle Beam Processing,” assigned to the assignee of the presentinvention, describes a suitable gas delivery system 2146. Another gasdelivery system is described in U.S. Pat. No. 5,435,850 to Rasmussen fora “Gas Injection System,” also assigned to the assignee of the presentintention. For example, iodine can be delivered to enhance etching, or ametal organic compound can be delivered to deposit a metal.

A micromanipulator 2147, such as the EasyLift micromanipulator from FEI,Hillsboro, Oreg., the assignee of the present invention, can preciselymove objects within the vacuum chamber. Micromanipulator 2147 maycomprise precision electric motors 2148 positioned outside the vacuumchamber to provide X, Y, Z, and theta control of a portion 2149positioned within the vacuum chamber. The micromanipulator 2147 can befitted with different end effectors for manipulating small objects. Inthe embodiments described below, the end effector is a thin probe 2150.The thin probe 2150 may be electrically connected to system controller2119 to apply an electric charge to the probe 2150 to control theattraction between a sample and the probe.

A door 2160 is opened for inserting work piece 2122 onto X-Y stage 2124,which may be heated or cooled, and also for servicing an internal gassupply reservoir, if one is used. The door is interlocked so that itcannot be opened if the system is under vacuum. In some embodiments, anatmospheric wafer handling system may be utilized. The high voltagepower supply provides an appropriate acceleration voltage to electrodesin ion beam focusing column 2116 for energizing and focusing ion beam2118. When it strikes work piece 2122, material is sputtered, that isphysically ejected, from the sample. Alternatively, ion beam 2118 candecompose a precursor gas to deposit a material. Focused ion beamsystems are commercially available, for example from FEI Company,Hillsboro, Oreg., the assignee of the present application. While anexample of suitable hardware is provided above, the invention is notlimited to being implemented in any particular type of hardware.

In this embodiment, material deposition can be carried out by forming aprotective capping material of two or more distinct layers. A user maychoose to deposit a “softer” material first, to be in direct contactwith the underlying substrate, and then a second, “harder” layer may bedeposited on top of the first layer. The harder top layer will resisterosion from the ion beam, while the softer bottom layer will preventcross-sectioning artifacts. In particular, if the bottom layer can bechosen to match the sputter rate of the underlying material, then therisk of cross-sectioning artifacts can be minimized. In other cases, theorder may be reversed, with the harder material deposited first,followed by the softer material. This arrangement may be preferred whenFIB milling hard materials such as diamond, carbon, or silicon carbide.

For example, as seen in FIG. 22, a lamella substrate 1200 has aprotective layer of material having a bottom layer 1202 that is firstdeposited preferably using electron beam induced deposition (EBID) ontothe top surface of substrate 1200 to prevent damage to the upper regionof the substrate 1200 near the top surface where the region of interestis generally located. An alternative is to use low energy (<8 keV) IBID,which also results in very low damage to the top surface. In someprocesses, a low-energy FIB deposition is used rather than an EBID. Thisfirst bottom layer material 1202 is chosen to match the etch rate of thematerial of substrate 1200 as closely as possible, particularly in the<5 kV FIB @ 10-45 degree off glancing angle operational regime. Forsilicon (Si)-based samples, this bottom layer 1202 is preferably a typeof silicon oxide material such as TEOS (IDEP), TEOS+H₂0 (IDEP2),TEOS+O₂, HMCHS, HMCHS+O₂ (IDEP3), HMCHS/H₂O and HMCHS/N₂O, TMCTS,TMCTS+O₂, and/or TMCTS/H₂O, TMCTS/N₂O. A top layer material 1204 is thendeposited on top of the bottom layer 1202 using ion beam induceddeposition (IBID). The top layer material 1204 is chosen to have a loweretch rate than the material of substrate 1200 to provide protectionduring the lamella thinning process and to prevent artifacts fromforming on the outer surfaces of the sample.

More than one top layer may be deposited, if desired. The top layer orlayers are preferably tungsten, carbon, or platinum. As an example,carbon has a superior resistance to low-kV FIB milling, which makes forexcellent protection, but has significant internal stress which can warpthe lamella. Therefore, a pure carbon layer is not desirable. However,as seen in FIG. 23, a substrate 1300 has protective layers including abottom layer 1302 of material similar to layer 1202 discussed inreference to FIG. 22. A thin layer of carbon 1304 (for example, a 100 nmlayer of C after 30 kV processing) on top of a thicker layer of tungsten1306 (for example, 400 nm or so) would survive low-kV FIB irradiationbetter than just tungsten alone and the tungsten would provide rigidityto the lamella. In the 35 degree grazing range, which is the angle ofthe FIB beam to lamella sidewall, the silicon substrate etch rateincreases dramatically compared to the tungsten which typically resultsin golf-tee effects that make the top part of the lamella much thickerthan the area a couple hundred nm below the sample surface. Aqualitative plot of the angle-dependent sputter rates of silicon andtungsten can be seen in the tables below.

Tables 1 and 2 below shows the sputter and volume yield from 5 kVgallium ions. The data from Tables 1 and 2 are charted in FIGS. 27A and27B.

TABLE 1 Sputter Yield (SRIM) Volume Yield, nm³/ion Angle Si W Si W 454.08 6.82 6.44E−05 1.37E−04 50 5.01 7.07 7.90E−05 1.42E−04 55 6.46 7.141.02E−04 1.43E−04 60 8.14 7.24 1.28E−04 1.45E−04 62 8.87 7.17 1.40E−041.44E−04 64 9.4 7.6 1.48E−04 1.53E−04 66 10.08 7.53 1.59E−04 1.51E−04 6810.99 7.54 1.73E−04 1.51E−04 70 11.6 7.44 1.83E−04 1.49E−04 75 12.947.29 2.04E−04 1.46E−04 80 13.22 6.55 2.09E−04 1.32E−04 82 12.63 6.11.99E−04 1.23E−04 84 12.09 5.65 1.91E−04 1.14E−04 85 11.47 5.47 1.81E−041.10E−04 86 10.68 5.04 1.69E−04 1.01E−04 87 9.992 4.72 1.58E−04 9.48E−05

TABLE 2 Sputter rate relative to Si at 45° Angle Si W 45 1.00 2.13 401.23 2.21 35 1.58 2.23 30 2.00 2.26 28 2.17 2.24 26 2.30 2.37 24 2.472.35 22 2.69 2.35 20 2.84 2.32 15 3.17 2.28 10 3.24 2.04 8 3.10 1.90 62.96 1.76 5 2.81 1.71 4 2.62 1.57 3 2.45 1.47

In another embodiment of the multilayer deposition strategy, numerouslayers may be depositing in an alternating configuration. Stackingmultiple layers of different deposition materials can result in a layerthat, as an average, has properties intermediate of the two individualcomponents. By adjusting the thicknesses of the individual components,as well as the total number of layers, the user may achieve some degreeof tunability, to achieve the desired property of the layer. Typically,the desired film property is intermediate of the individual components.For example, if platinum is too soft and carbon is too hard for aparticular application, a multilayer deposition of alternating platinumand carbon depositions may be preferred to a homogeneous layer of eitherof the individual components.

FIG. 24 shows such an embodiment of material deposition in whichsubstrate 1400 includes a protective layer 1402 with alternating layersof material 1404, 1406 in which the etch rate of the protective layermaterial 1402 is “tuned” by depositing the alternating, thin layers ofmaterial 1404, 1406 using discrete gas chemistries, which forms analternating “parfait-like” macrostructure with an etch rate that isbetween the etch rates of the individual components.

FIG. 25 shows an image of a substrate 1500 having a sacrificialprotective layer 1502 of discrete layers including a layer of tungsten1504 for visual observation of the delineation between the top ofsubstrate 1500 and protective layer 1502, a sacrificial layer of SEMdeposited silicon oxide 1506 and a top layer 1508 of tungsten. As can beseen, after thinning the “golf tee” effect occurs within the sacrificialprotective layer 1502 and not within substrate 1500.

FIG. 26 shows a silicon lamella with an EBID TEOS layer, an IBIDtungsten layer, and an IBID carbon layer.

In the embodiments of FIGS. 12-16, the sacrificial protective layer withsimilar etch rates to the substrate sample moves the golf-tee up intothe protective layer and away from the top of substrate that includesthe area of interest for observation and analysis.

As seen in FIG. 28, the present invention provides a method of materialdeposition in which a sample is loaded into a selected beam system at1600. At least two precursor gases are provided for material deposition1602. In decision block 1604 it is determined whether to depositmaterial in distinct layers or as a composite layer. If distinct layersare deposited 1606, a first layer is deposited on the sample 1608followed by another layer 1610. If only two layers are to be depositedthe decision to end 1612 is determined at 1616 and the process isfinished 1618. If more than two layers are to be deposited the decisionnot to end 1614 is made and the process returns to block 1608 andcontinues until it is determined to end 1616 and finish the process1618. If a composite layer is to be deposited 1620 then at least twoprecursor gases are mixed 1622 according to the determined recipe andthe composite layer is deposited 1624 onto the sample and the process isended 1626.

Some embodiments of the invention provide a method of materialdeposition onto a sample; comprising,

loading a substrate into a charged particle beam system, the substratecontaining a region of interest; and

directing a charged particle beam toward the substrate to inducedeposition from a precursor gas of a protective layer above the regionof interest, wherein the sputter rate of the protective layersubstantially matches the sputter rate of the substrate.

In some embodiments, the protective layer includes distinctive layers ofdifferent material.

In some embodiments, one layer is a silicon oxide deposition.

In some embodiments, one layer is tungsten, carbon, or platinum.

In some embodiments, the protective layer includes alternating layers ofmaterial.

In some embodiments, after thinning the sample has opposed faces thatare substantially orthogonal below the protective layer.

In some embodiments, the first protective layer has a sputter rate thatclosely matches the sputter rate of the sample and a second protectivelayer has a sputter rate that is lower than the sputter rate of thesample.

In some embodiments, the protective layer is a composite mix of materialhaving a sputter rate that substantially matches the sputter rate of thesubstrate.

Some embodiments of the invention provide an apparatus for materialdeposition onto a sample, comprising;

an ion beam system including an ion beam source, optics for focusing anion beam along an axis and onto a substrate, and a micromanipulator formanipulating a sample; and

a computer-readable memory storing computer instructions, theinstructions including a program for controlling the apparatus andcausing the apparatus to carry out the steps of:

loading a substrate into an ion beam system; and

directing a charged particle beam toward the substrate to inducedeposition from one or more precursor gases to form a protective layeron the sample, the protective layer being composed of at least twomaterials that have been formulated and arranged according to thematerial properties of the sample.

Some embodiments provide a method of material deposition onto a sample;comprising:

directing a charged particle beam toward the sample to induce materialdeposition onto the sample to form a protective layer, wherein theprotective layer combines the properties of at least two precursors.

In some embodiments, the protective layer includes alternating layers ofdifferent materials.

In some embodiments, the protective layer is a composite mix ofdifferent materials.

Although the description of the present invention above is mainlydirected at a method of material deposition, the method robust,repeatable and therefore suitable for automation, it should berecognized that an apparatus performing the operation of the methodwould further be within the scope of the present invention. Although thematerial deposition methods have been described as being performed witha dual-beam system, it should be understood that the material depositionmethods described herein may be performed by a stand-alone SEM system orstand-alone FIB system of any ion polarity. It should be furtherunderstood that most beam depositions are not completely pure but maycontain “impurities” such as precursor fragments, hydrocarbonincorporation, voids, and density variations that can cause deviationsfrom theoretical models of sputter hardness. Further, it should berecognized that embodiments of the present invention can be implementedvia computer hardware or software, or a combination of both. The methodscan be implemented in computer programs using standard programmingtechniques—including a computer-readable storage medium configured witha computer program, where the storage medium so configured causes acomputer to operate in a specific and predefined manner—according to themethods and figures descried in this Specification. Each program may beimplemented in a high level procedural or object oriented programminglanguage to communicate with a computer system. However, the programscan be implemented in assembly or machine language, if desired. In anycase, the language can be a compiled or interpreted language. Moreover,the program can run on dedicated integrated circuits programmed for thatpurpose.

A preferred method or apparatus of the present invention has many novelaspects, and because the invention can be embodied in different methodsor apparatuses for different purposes, not every aspect need be presentin every embodiment. Moreover, many of the aspects of the describedembodiments may be separately patentable. The invention has broadapplicability and can provide many benefits as described and shown inthe examples above. The embodiments will vary greatly depending upon thespecific application, and not every embodiment will provide all of thebenefits and meet all of the objectives that are achievable by theinvention.

It should be recognized that embodiments of the present invention can beimplemented via computer hardware, a combination of both hardware andsoftware, or by computer instructions stored in a non-transitorycomputer-readable memory. The methods can be implemented in computerprograms using standard programming techniques—including anon-transitory computer-readable storage medium configured with acomputer program, where the storage medium so configured causes acomputer to operate in a specific and predefined manner—according to themethods and figures described in this Specification. Each program may beimplemented in a high level procedural or object oriented programminglanguage to communicate with a computer system. However, the programscan be implemented in assembly or machine language, if desired. In anycase, the language can be a compiled or interpreted language. Moreover,the program can run on dedicated integrated circuits programmed for thatpurpose.

Further, methodologies may be implemented in any type of computingplatform, including but not limited to, personal computers,mini-computers, main-frames, workstations, networked or distributedcomputing environments, computer platforms separate, integral to, or incommunication with charged particle tools or other imaging devices, andthe like. Aspects of the present invention may be implemented in machinereadable code stored on a non-transitory storage medium or device,whether removable or integral to the computing platform, such as a harddisc, optical read and/or write storage mediums, RAM, ROM, and the like,so that it is readable by a programmable computer, for configuring andoperating the computer when the storage media or device is read by thecomputer to perform the procedures described herein. Moreover,machine-readable code, or portions thereof, may be transmitted over awired or wireless network. The invention described herein includes theseand other various types of non-transitory computer-readable storagemedia when such media contain instructions or programs for implementingthe steps described above in conjunction with a microprocessor or otherdata processor. The invention also includes the computer itself whenprogrammed according to the methods and techniques described herein.

Computer programs can be applied to input data to perform the functionsdescribed herein and thereby transform the input data to generate outputdata. The output information is applied to one or more output devicessuch as a display monitor. In preferred embodiments of the presentinvention, the transformed data represents physical and tangibleobjects, including producing a particular visual depiction of thephysical and tangible objects on a display.

The terms “work piece,” “sample,” “substrate,” and “specimen” are usedinterchangeably in this application unless otherwise indicated. Further,whenever the terms “automatic,” “automated,” or similar terms are usedherein, those terms will be understood to include manual initiation ofthe automatic or automated process or step.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” To theextent that any term is not specially defined in this specification, theintent is that the term is to be given its plain and ordinary meaning.The accompanying drawings are intended to aid in understanding thepresent invention and, unless otherwise indicated, are not drawn toscale. Particle beam systems suitable for carrying out the presentinvention are commercially available, for example, from FEI Company, theassignee of the present application.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made to the embodiments described herein withoutdeparting from the scope of the invention as defined by the appendedclaims. Moreover, the scope of the present application is not intendedto be limited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

We claim as follows:
 1. A method of charged particle beam processing ofa substrate, comprising: providing a first precursor gas to thesubstrate, and directing a charged particle beam toward the substrate toinduce deposition of a first protective layer above a region of intereston the substrate surface, the first protective layer having a firstsputter rate; providing a second precursor gas to the substrate, anddirecting the charged particle beam toward the substrate to inducedeposition of a second protective layer on the first protective layer,the second protective layer having a second sputter rate; providing athird precursor gas to the substrate, and directing the charged particlebeam toward the substrate to induce deposition of a third protectivelayer on the second protective layer, the third protective layer havinga third sputter rate, wherein the first sputter rate is different fromthe second sputter rate, and the second sputter rate is different fromthe third sputter rate; and directing a second charged particle beamtoward the substrate to mill through the first protective layer, thesecond protective layer and the third protective layer to expose theregion of interest.
 2. The method of claim 1, wherein the second sputterrate is lower than the first sputter rate.
 3. The method of claim 1,wherein the third sputter rate is lower than a sputter rate of thesubstrate.
 4. The method of claim 1, wherein the first sputter rate isthe same as the third sputter rate.
 5. The method of claim 4, furthercomprising: before directing the charged particle beam towards thesubstrate, providing the second precursor gas to the substrate, anddirecting the charged particle beam toward the substrate to inducedeposition of a fourth protective layer on the third protective layer.6. The method of claim 5, further comprising while providing the chargedparticle beam to induce deposition, adjusting a thickness of at leastone of the first, second, and third protective layers based on a sputterrate of the substrate.
 7. The method of claim 1, wherein the chargedparticle beam is an electron beam or an ion beam.
 8. The method of claim1, wherein the second charged particle beam is an ion beam.
 9. Themethod of claim 1, further comprising selecting the first precursor gasbased on a sputter rate of the substrate.
 10. An apparatus forprocessing of a substrate to expose for observation a region ofinterest, comprising: a sample stage for positioning a substrate; an ionbeam system for providing an ion beam towards the substrate; a gasdelivery system for providing precursor gases to the substrate; and acontroller with programmed instructions stored in a computer readablememory causing the apparatus to: provide a first precursor gas, anddirect the ion beam toward the substrate to induce deposition of a firstprotective above the region of interest on the substrate surface, thefirst protective layer having a first sputter rate; provide a secondprecursor gas, and direct the ion beam toward the substrate to inducedeposition of a second protective on the first protective layer, thesecond protective layer having a second sputter rate; provide a thirdprecursor gas, and direct the ion beam toward the substrate to inducedeposition of a third protective layer on the second protective layer,wherein the third protective layer having a third sputter rate, thefirst sputter rate is different from the second sputter rate, and thesecond sputter rate is different from the third sputter rate; and directthe ion beam toward the substrate to mill through the first protectivelayer, the second protective layer and the third protective layer toexpose the region of interest.
 12. The apparatus of claim 11, whereinthe second sputter rate is lower than the first sputter rate.
 13. Theapparatus of claim 11, wherein the third sputter rate is lower than asputter rate of the substrate.
 14. The apparatus of claim 11, whereinthe first sputter rate is the same as the third sputter rate.
 15. Theapparatus of claim 14, wherein the controller with further programmedinstructions causing the apparatus to: after deposition of the thirdprotective layer, provide the second precursor gas to the substrate, anddirect the ion beam toward the substrate to induce deposition of afourth protective layer on the third protective layer.
 16. The apparatusof claim 11, wherein the controller with further programmed instructionscausing the apparatus to: select the first precursor gas based on asputter rate of the substrate.